A wide variety of apparatus adapted to lock clamp members or collar members onto smooth shafts have been known in the art, including (but not limited to) radially disposed "grub screws"; locking rings which pivot in a manner such that attempted movement along the shaft results in the locking ring/s being forced into tighter contact with the shaft through a cantilever action; interlocking cones which can be wedged either actively or passively, into frictional engagement with the shaft and one another; bands which can be constricted around the shaft by means of threads or cam-lever systems.
These apparatus suffer from one or more of the following deficiencies: they are relatively expensive to manufacture; they can damage the surface of the shaft because of point loadings with hard materials; they often need a tool in order to be adjusted; they may be restricted to locking the collar in one direction only; they may be sensitive to changes in the frictional coefficients of the mating materials induced by the presence of moisture or oil; they are often non-self-locking so they rely on the original clamping force generated and are thus susceptible to the effect of creep in materials caused by high temperatures and/or prolonged used; they are commonly bulky in design and can be slow and/or difficult to adjust.
It is accordingly an object of this invention to provide a clamp member and a method of locking a clamp member onto an elongate member which goes at least some way towards overcoming the problems with apparatus known in the art.
According to this invention there is provided a clamp member including a collar member including a internal shaft, the internal shaft comprising a longitudinal recess to accommodate a substantially circular (in cross section) elongate member and at least one integral recess tapered with respect to the longitudinal axis of the elongate member; and at least one wedge member adapted, in use, to be positioned in the integral recess of the collar member between the inner surface of the collar and the surface of the elongate member; wherein the inner surface of said wedge member is shaped to provide at least two spaced apart areas of contact with the elongate member which areas of contact have tangent planes which are at an oblique angle one to the other; and wherein the outer surface of the wedge member is shaped to substantially correspond with the recess in the collar member, to provide an interface in which the included angle defined by any tangent planes of the recess-wedge interface substantially exceeds the included angle defined by any tangent planes to the elongate member-wedge member interface area, the arrangement being such that, in use the inner surface of the wedge member is substantially aligned with the surface of the elongate member by movement of the collar member in one direction, whereupon the two spaced apart areas of contact on the inner surface of the wedge member are frictionally engaged on the elongate member and the inner surface of the collar member is moved into frictional engagement with the outer surface of the wedge member to frictionally engage the collar member on the clamp member and elongate member; the clamp member being disengageable from the elongate member by moving the collar member in the opposite direction.
According to a further aspect of this invention there is provided a clamp member as described in the preceding paragraph wherein the longitudinal recess is tapered outwardly from one or both ends of the collar member and wherein the wedge member has an inner surface engageable with the elongate member and an outer surface which is tapered from both ends substantially to correspond with the taper of the inner surface of the collar member.
According to a further aspect of the invention the longitudinal recess in the clamp member is tapered from one or both ends of the collar member and wherein the inner surface of the wedge member is, in cross section, of a lesser radius than the radius of the substantially circular (in cross section) elongate member to be inserted therein, the wedge member thus being adapted to contact the surface of the elongate member at the two areas of contact, the tangents of which are disposed at an oblique angle one to the other, the outer surface of the wedge member being tapered from both ends substantially to correspond with the taper of the inner surface of the collar member.
In a further preferred embodiment of the invention the wedge member is constructed from an at least partially resilient material, in order that outer portions of the curved inner surface of the wedge member are adapted to be wedged at least partially apart, in use, the wedge member thus being adapted to be held in constant compression within the recess in the collar member, in order to accommodate variations in the diameter of the elongate member or surface irregularities of the elongate member.
A further possible embodiment the clamp member includes an upstanding ridge or a recess on the inner surface of the wedged member, the ridge or the recess being positioned substantially between the two spaced apart areas of contact of the wedge member, the ridge or recess portion being adapted to engage a corresponding recess or ridge provided on the surface of the elongate member, the arrangement being such that the inner surface of the wedge member is engageable with the elongate member, while at the same time the collar member is moveable relative to the outer surface of the wedge member.
In one preferred application of the invention the clamp member is adapted to engage an elongate member in the form of a substantially circular (in cross section) fibreglass fencepost, wherein the collar member is provided with appropriate means to locate a fence wire, and wherein the collar member and wedge member are formed of an at least partially resilient plastic material which enables the clamp member to accommodate variations in the outer circumference of the substantially circular fence post.
Further according to this invention there is provided a method of clamping a clamp member on an elongate member, wherein said clamp member includes a collar member with an internal shaft, the internal shaft comprising a longitudinal recess to accommodate an elongate member and least one integral recess tapered with respect to the longitudinal axis of the elongate member, and at least one wedge member adapted to be positioned in the integral recess in the collar member between the inner surface of the collar member and the surface of the elongate member, comprising the steps of the substantially aligning the inner surface of the wedge member with the surface of the elongate member by movement of the collar member in a first direction, the inner surface of the wedge member becoming frictionally engaged with the surface of the elongate member and the collar member becoming frictional engaged with the tapered outer surface of the wedge member, thereby clamping on to the elongate member, and wherein the clamp member is disengageable from the elongate member by movement in the opposite direction.